1. Field of the Invention
The present invention relates to a method for making an optically active diphosphine ligand for use in the synthesis of a complex, which in turn is useful as a catalyst for a variety of asymmetric synthesis reactions.
2. Description of the Prior Art
Heretofore, many transition metal complexes have been reported for use in asymmetric synthesis reactions such as asymmetric hydrogenation, asymmetric isomerization and asymmetric hydrosilylation. In particular, many complexes which comprise a transition metal, such as ruthenium, rhodium, iridium or palladium, coordinated with an optically active tertiary phosphine compound, have superior characteristics as a catalyst for asymmetric synthesis reactions. In order to further improve the catalytic performance of these complexes, many phosphine compounds having special structures have been developed (see, for example, "Chemistry of Organometallic Complexes", Introductory Chemistry 32, pp. 237-238, Ed. Chemical Society of Japan, 1982 and "Asymmetric Catalysis in Organic Synthesis", R. Noyori, A Wiley-Interscience Publication, 1996).
In particular, 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (hereinafter referred to as BINAP) is an excellent optically active phosphine. A rhodium complex (Japanese Patent Application Laid-Open (hereinafter referred to as "JP-A") No. 55-61,973) having BINAP as a ligand and a ruthenium complex (JP-A No. 61-6,390) having BINAP as a ligand have been reported. Furthermore, a rhodium complex (JP-A No. 60-199,898) having 2,2'-bis(di(p-tolyl)phosphino)-1,1'-binaphthyl (hereinafter referred to as p-Tol-BINAP) as a ligand and a ruthenium complex (JP-A No. 61-63,690) having the same ligand have each been reported as providing excellent effects in asymmetric hydrogenation and isomerization reactions. Additionally, JP-A No. 4-139,140 discloses a ruthenium complex comprising 2,2'-bis(diphenylphosphino)-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl (hereinafter referred to as H8-BINAP) as a ligand, and reports that this complex provides an excellent effect in an asymmetric hydrogenation reaction.
An industrial method hitherto known for making the above phosphine compounds consists of the procedure illustrated by the following reaction steps: brominating a racemic binaphthol (7) by means of triphenylphosphine dibromide at a high temperature (240 to 320.degree. C.) to prepare compound (8), forming a Grignard reagent (9) from the compound (8), condensing the Grignard reagent (9) with a diarylphosphinyl chloride to produce a phosphine dioxide (10), optical resolving the phosphine dioxide (10) to prepare compound (11), and reducing compound (11) by means of a reducing agent such as trichlorosilane to a tertiary phosphine compound (a type of BINAP compound) (1b) (H. Takaya, K. Mashima, K. Koyano, M. Yagi, H. Kumobayashi, T. Taketomi, S. Akutagawa, and R. Noyori, J. Org. Chem., 1986, Vol. 51, pp. 629) . ##STR2## where the double line having a continuous line and a dotted line represents a double bond or a single bond such that the ring having the double line forms a naphthalene ring or an octahydronaphthalene ring with an adjacent benzene ring; and Ar represents a phenyl group, a substituted phenyl group (having 1 to 3 substituent groups, which may be the same or different, selected from the group consisting of a halogen atom, a lower alkyl group, a lower alkoxy group and a halogenated lower alkyl group) or a naphthyl group which may have a lower alkyl or lower alkoxy substituent.
Another method comprises hydrogenating binaphthyl bromide to prepare 5,5',6,6',7,7',8,8'-octahydrobinaphthyl bromide, forming a Grignard reagent from the octahydrobinaphthyl bromide, condensing the Grignard reagent with a diarylphosphinyl chloride to produce a phosphine dioxide, optical resolving the phosphine dioxide, and reducing the resulting compounds by means of a reducing agent such as trichlorosilane to a tertiary phosphine compound (H8-BINAP) (X. Zhang, K. Mashima, K. Koyano, N. Sayo, H. Kumobayashi, S. Akutagawa, and H. Takaya, J. Chem. Soc. Perkin Trans. 1, 1994, p.2309). Yet another method comprises preparing 2,2'-bis(trifluoromethanesulfonyloxy)-1,1'-binaphthyl by using an optically active binaphthol and reacting the 2,2'-bis(trifluoromethanesulfonyloxy)-1,1'-binaphthyl with diphenylphosphine in the presence of a nickel/phosphine complex to obtain BINAP (Dongwei Cai, Joseph F. Pyyack, Dean R. Bender, David L. Hughes, Thomas R. Verhoeven, and Paul J. Reider, J. Org. Chem., 1994, Vol. 59, p. 7180).
However, each of above described methods for making an optically active phosphine compound has a problem. For example, in the method of Takaya et al., the reaction vessel is limited, because a high temperature is necessary for brominating binaphthol and because hydrobromic acid is generated in this step. Furthermore, the method by Takaya et al. and the method by Zhang et al. are disadvantageous in that a high temperature and a high hydrogen pressure are also necessary in the hydrogenation reaction of binaphthyl bromide. Also, these methods are uneconomical if only one of the enantiomers is needed, because these methods require optical resolution of the racemic reaction product. In addition, there are many racemic reaction products whose optical resolution is difficult. Besides, the method by Dongwei et al. presents a problem in that diphenylphosphine, which is used in the reaction of this method, is undesirably used in a large amount in industry due to its insufficient stability (diphenylphosphine is readily oxidized) and toxicity. However, this method does not require optical resolution.